Knowledge Bank

We have recently observed the two-photon spectrum of pyridine in the region 2780 to 2980 {\AA}. The four strong bands observed in the one-photon spectrum (origin, $0-0+139cm-1,0-0+\nu 6a,0-0+\nu 6a+139cm-1)$ are also observed in the two-photon spectrum with different rotational contours. The assignment by D.A. Ramsay and co-workers of the $139cm-1$ band to the ``boat’’ vibration, $\nu 16b$, is consistent with our observations. Polarization and rotational contour studies will be discussed in light of this assignment.